Apparatus and method for implanting an arteriovenous graft

ABSTRACT

An apparatus is provided for subcutaneous implantation in a patient using a tunneling instrument. The implantation apparatus comprises a vascular graft and a connector adapted to couple a distal end of the tunneling instrument and a proximal end of the graft. The connector comprises a tip, a first end of the tip configured to be received within the proximal end of the graft, a clip for securing the graft to the tip, and a coupler for a rotatable connection of the tip to the tunneling instrument such that the tip is rotatable about its longitudinal axis relative to the coupler to facilitate attachment of the graft to the tunneling instrument. The implantation apparatus may further comprise a removable sheath configured to substantially cover the length of the graft.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.16/723,211, filed Dec. 20, 2019, which claims the benefit of U.S.Provisional Application No. 62/783,187, filed Dec. 20, 2018, and U.S.Provisional Application No. 62/940,438, filed Nov. 26, 2019, thecontents of all of which are incorporated herein in their entirety.

BACKGROUND

An apparatus and method are described for implanting an arteriovenousgraft and, more particularly, an apparatus and method for use in forminga subcutaneous anatomical tunnel for implanting the arteriovenous graft,including use of a removable sheath enclosing the graft duringimplantation.

An arteriovenous graft is a tubular device that is suitable forimplantation in the body to redirect flow of blood between bloodvessels. Surgical implantation of the arteriovenous graft requiresplacement of the graft within subcutaneous tissue. An initial step inthe implantation procedure is the creation of a subcutaneous anatomicpathway for the arteriovenous graft, which is commonly called a grafttunnel, between anastomotic sites for passage of the vascular graft.This is a required surgical step in peripheral vascular procedures forall peripheral, vascular access and extra-anatomical graft locations.The arteriovenous graft is positioned in the tunnel within the bodilytissue for fixation of the graft to an existing peripheral vessel toform a bypass around the vessel, or a portion thereof, or connection ofan artery and vein to form an arteriovenous shunt. The vascular graftmay also connect an artery to an artery.

A conventional tunneling device includes an elongated rigid rod having ahandle on a proximal end and a bullet-shaped tip at a distal end. Therod may vary in size and shape and may have a straight shaft, a curvedshaft or a semicircular shaft, which allows for a variety of graftplacement positions and locations. In the tunneling procedure, aproximal incision and a distal incision are made at a chosen area ofanastomosis. The tip at the distal end of the tunneling device isinserted into the proximal incision. The tip of the tunneling device isthen forcefully passed through the subcutaneous tissue creating a pathbetween the incisions by blunt dissection until the tip protrudes fromthe distal incision. Once the tip is exposed, a proximal end of thearteriovenous graft is tied onto the distal end or the tip of thetunneling device with sterile suture thread. The tunneling instrumentand attached arteriovenous graft are then pulled along the path throughthe recently dissected graft tunnel until the proximal end of thearteriovenous graft extends from the proximal incision. When thearteriovenous graft is appropriately positioned, the graft is cut freefrom the distal end of the tunneling instrument. An anastomosis isformed around the area of vasculature to be bypassed and the incisionsare closed.

The step of pulling the tunneling instrument and attached arteriovenousgraft through the graft tunnel requires significant force. The forcerequired depends on a number of factors, including the relative sizes ofthe graft tunnel and the graft and the material of the graft.Conventional delivery systems for venous and other implantable devicesare sometimes covered by a retaining sheath that reduces the friction ofpassage through the subcutaneous tissue. Following implantation, thesheath is removed by rolling back over the device in order to retractthe sheath. A pull member may be provided and connected to the sheath toretract the sheath. In one application, the sheath is folded back ontoitself so as to provide an inner sheath and an outer sheath disposedover and extending axially along the device. The outer sheath isattached to the pull member. As the pull member is pulled, the outersheath moves with it causing the sheath to “roll” with respect to thedevice, thereby progressively uncovering the device. However, whilerolling a sheath during retraction reduces the necessary pulling forceas compared to withdrawing the sheath by sliding the sheath over thedevice, there is still significant force necessary to retract a sheathfollowing implantation of an arteriovenous graft.

For the foregoing reasons, there is a need for an apparatus and methodfor implanting an arteriovenous graft for minimizing trauma to tissue.The arteriovenous graft may be enclosed within a flexible, expandablesheath configured to surround a length of the tunneling device or thegraft. The sheath may be coated on an outside surface with a lubricioussubstance to provide a low coefficient of friction, allowing the sheathand tunneling device to be easily pushed through tissue. The sheathshould be retractable in a reliable manner with a low pulling force forminimizing problems associated with excessive axial forces on the sheathduring retraction. The tunneling device should be capable of use withany type of vascular graft including, but not limited to, a naturaltissue graft. The apparatus may comprise a tunneling device that allowsfor delivery of fluid adjacent to the tip during the tunneling process.

SUMMARY

An apparatus is provided for subcutaneous implantation in a patientusing a tunneling instrument, including a shaft having a proximal endand a distal end. The implantation apparatus comprises a vascular grafthaving a proximal end and a distal end and a length between the proximalend and the distal end. A connector is adapted to couple the distal endof the tunneling instrument and the proximal end of the graft. Theconnector comprises a tip, a first end of the tip configured to bereceived within the proximal end of the graft, a clip for securing thegraft to the tip, and a coupler for a rotatable connection of the tip tothe tunneling instrument such that the tip is rotatable about itslongitudinal axis relative to the coupler to facilitate attachment ofthe graft to the tunneling instrument.

In one aspect, the coupler comprises a screw thread formed on anexternal surface for connection of the coupler to the tunnelinginstrument. In a further aspect, the coupler comprises a ferruledefining an axial passage for rotatably receiving a proximal end of thetip.

In one embodiment, the implantation apparatus further comprises aremovable sheath configured to substantially cover the length of thegraft.

In another embodiment, the tip comprises a body including anintermediate portion having a reduced diameter forming a circumferentialgroove around a periphery, and wherein the clip is positioned in thegroove, a portion of the graft being positioned between the clip and thetip within the groove, the clip being crimped about the tip to fix thegraft to the tip. The clip is sized and shaped to provide a snap-fitconnection within the groove.

In an alternative embodiment, the tip is adapted to be removablyattached to the distal end of the tunneling instrument, and wherein theconnector is configured for connecting the graft to the tunnelinginstrument upon removal of the tip. In one aspect, the coupler comprisesa frustoconical cone having an axial opening for receiving the graft, alength of the cone including a screw thread formed on an externalsurface for connection of the cone to the tunneling instrument, whereina portion of the graft is positioned between the threads of the cone andthe tunneling instrument to fix the graft to the tip. In another aspect,the coupler comprises a hollow sleeve for rotatable connection to thetunneling instrument, and a plug received within the proximal end of thegraft. The sleeve is configured for receiving the plug such that aportion of the graft is positioned between the plug and the sleeve tofix the graft in the sleeve.

The coupler is adapted to be attached to a synthetic vascular graft, anatural tissue vascular graft or an arteriovenous graft.

An implantable device is also provided for subcutaneous delivery in apatient using a tunneling instrument including a shaft having a proximalend and a distal end. The implantable device comprises a vascular grafthaving a length, a distal end, a proximal end, an outer surface and alongitudinal axis. A sheath having a length is positioned over asubstantial portion of the outer surface of the vascular graft. Thesheath has longitudinally spaced perforations along the length of thesheath for permitting tearing of the sheath. The sheath is configured toevert upon application of a longitudinal force to the sheath followingimplantation of the vascular graft to cause the sheath to move in aproximal direction during removal of the sheath from the implantedgraft. Upon eversion and exceeding a tearing strength, the sheath tearsprogressively along the perforations that are generally oriented in alinear arrangement along the length of the sheath.

In one aspect, two rows of perforations are generally orientedcircumferentially opposite to one another. In another aspect, two rowsof perforations are generally oriented adjacent and parallel to oneanother.

In one embodiment, the implantable device further comprises a tetherconnected to the sheath for applying a pulling force in a proximaldirection. One end of the tether may be attached to the sheath at aposition adjacent to the distal end of the sheath.

In another embodiment, a sheath having perforations is folded back onitself forming a double wall having an inner portion and an outerportion. The sheath is configured to slide over itself upon applicationof a longitudinal force to the sheath following implantation of thevascular graft to cause the sheath to tear along the perforations whilemoving in a proximal direction during removal of the sheath from theimplanted graft thus reducing the force necessary to extract the sheath.

A tunneling device is provided for delivery of fluid from a fluid sourcefor use in the subcutaneous placement of a vascular graft in a patient.The tunneling device comprises a rigid hollow rod for forming asubcutaneous path and having a distal end, a proximal end and aninterior lumen defining a fluid pathway. The interior lumen is adaptedto be in fluid communication with the fluid source. A hollow tapered tipis mounted to the distal end of the rod and has an interior lumen influid communication with the lumen in the rod. One of the rod or the tipdefines at least one opening for delivery of fluid from the fluid sourcethrough the at least one opening.

Another tunneling device is provided for use in the subcutaneousplacement of a vascular graft for attachment to a blood vessel in apatient. The tunneling device comprises a rigid rod having a proximalend and a distal end for forming a subcutaneous path. A magnetic taperedtip is at the distal end of the rod. A magnetic wand magneticallyengages the tip from external to the skin for longitudinal advancementof the rod and tip along the subcutaneous path.

Yet another tunneling device is provided for use in the subcutaneousplacement of a vascular graft in a patient. The tunneling devicecomprises a rigid helical rod having a proximal end and a distal end. Atapered tip is mounted to the distal end of the rod. In use, the rodforms a helical tunnel when rotated during longitudinal advancementalong a subcutaneous path.

A method is provided for using a tunneling device having a distal tipfor placement of a vascular graft along a subcutaneous path in apatient. The tunneling device method comprises the steps of forming anincision adjacent to a chosen area of anastomosis and placing markers onthe skin indicating a predetermined subcutaneous path. The tunnelingdevice is inserted in the incision for performing blunt dissection ofsubcutaneous tissue along the path indicated by the markers with thetunneling device. A proximal end of the graft is attached to thetunneling device followed by the step of retracting the tunneling devicefrom the incision until the proximal end of the graft exits theincision. The graft is released from the tunneling device andanastomoses are formed of the ends of the graft to a first blood vesseland a second blood vessel and then the incision is closed. In oneaspect, the tip of the tunneling device may be removed before attachingthe graft.

Still another tunneling device is provided for use in subcutaneousplacement of a vascular graft in a patient. The tunneling devicecomprises a guide wire and a hollow inflatable conduit coaxiallysurrounding the guide wire over a substantial portion of its length. Theconduit in a delivery configuration collapses against the wire due toconfining pressure when inserted subcutaneously into a body. Inflationof the conduit radially expands the conduit to a deployed configurationand spaces the conduit from the wire over substantially the full lengthof the wire and preventing collapse of the subcutaneous tissue inwardlyagainst the wire. The graft may be introduced into the conduit while theconduit is inflated.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the apparatus and method for use informing a subcutaneous anatomical tunnel, reference should now be had tothe embodiments shown in the accompanying drawings and described below.In the drawings:

FIG. 1 is a side perspective view of a tunneling instrument including anembodiment of a tip assembly.

FIG. 2 is a close-up side perspective view of a distal portion of thetunneling instrument and the tip assembly as shown in FIG. 1.

FIG. 3 is a distal end perspective view of the portion of the tunnelinginstrument and the tip assembly as shown in FIG. 2.

FIG. 4 is a side elevation view of the tip assembly as shown in FIGS.1-3.

FIG. 5 is an exploded side elevation view of the tip assembly as shownin FIG. 4.

FIG. 6 is a distal end perspective view of an embodiment of a tip foruse with the tip assembly as shown in FIG. 4.

FIG. 7 is a side elevation view of the tip as shown in FIG. 6.

FIGS. 8 and 9 are distal and proximal end perspective views of anembodiment of a swivel connector for use with the tip assembly as shownin FIG. 4.

FIG. 10 is a front, side and rear perspective views of an embodiment ofa graft clip for use in the tip assembly shown in FIG. 4.

FIG. 11 is a side elevation view of the tip assembly and graft clip asshown in FIG. 10.

FIG. 12 is an exploded side perspective view of the tip and graft clipas shown in FIG. 11.

FIG. 13 is a front perspective view of another embodiment of a graftclip in a first closed position for use with the tip assembly as shownin FIG. 4.

FIG. 14 is a front perspective view of the graft clip as shown in FIG.13 with the graft clip in a second open position.

FIG. 15 is a front perspective view of the graft clip as shown in FIG.14 with the graft clip in the open position on the tip assembly as shownin FIG. 4.

FIG. 16 is a front perspective view of the graft clip as shown in FIG.13 with the graft clip in a second closed position on the tip assembly.

FIG. 17 is a side perspective view of the graft clip as shown in FIG. 14with the graft clip in the open position on the tip assembly as shown inFIG. 4 and surrounding a proximal end of an AVG.

FIG. 18 is a side perspective view of the graft clip as shown in FIG. 13with the graft clip in a second closed position on the tip assembly overthe proximal end of the AVG.

FIG. 19 is an exploded perspective view of an embodiment of a couplerfor connecting a proximal end of an arteriovenous graft to a distal endof a tunneling device.

FIG. 20 is a side perspective views of another embodiment of a tunnelingdevice including a frustoconical hood showing steps for use as a couplerfor connecting a proximal end of an arteriovenous graft to a distal endof a tunneling device.

FIG. 21 is a perspective view of a sheath surrounding at least asubstantial portion of an arteriovenous graft and secured with the AVGto the tip assembly and tunneling instrument as shown in FIG. 1 usingthe clip as shown in FIG. 13.

FIG. 22 is a close-up of the perspective view of the sheath andarteriovenous graft connected to the tip assembly and tunnelinginstrument as shown in FIG. 21.

FIGS. 23A-23C are schematic views of an arteriovenous graft enclosedwithin an embodiment of a removable sheath with a proximal end of thecombined graft and sheath attached to the tip assembly on a tunnelinginstrument.

FIG. 24A and 24B are schematic views of an arteriovenous graft enclosedwithin another embodiment of a removable sheath with a proximal end ofthe combined graft and sheath attached to the tip assembly on atunneling instrument.

FIGS. 25A-25C are schematic views of an arteriovenous graft enclosedwithin a third embodiment of a removable sheath with a proximal end ofthe combined graft and sheath attached to the tip assembly on atunneling instrument.

FIG. 26 is a side perspective view of another embodiment of a tipassembly and tunneling instrument for use in forming a subcutaneousanatomical tunnel for implantation of a vascular graft.

FIG. 27 is a side perspective view of a third embodiment of a tipassembly and tunneling instrument for use in forming a subcutaneousanatomical tunnel for implantation of a vascular graft.

FIG. 28 is a side perspective view of a fourth embodiment of a tipassembly and tunneling instrument for use in forming a subcutaneousanatomical tunnel for implantation of a vascular graft including amagnetic tip portion and a wand.

FIG. 29 is a schematic front elevation view of an embodiment of anapparatus for use in forming a subcutaneous anatomical tunnel forimplantation of a vascular graft using a self-guided tunneling device.

FIGS. 30 and 31 are schematic front elevation views of an embodiment ofan apparatus for use in forming a subcutaneous anatomical tunnel forimplantation of a loop vascular graft using two-piece tunneling devicehaving a distal locking mechanism.

FIG. 32 is a side perspective view of an embodiment of an apparatus foruse in forming a subcutaneous anatomical tunnel for implantation of avascular graft using a helical tunneling device.

FIG. 33 is a side perspective view of an embodiment of a tunnel formingapparatus showing a guide wire and a sheath.

FIG. 34 is a side perspective view of the tunnel forming apparatus asshown in FIG. 30 with the guide wire fully received within the sheath.

FIG. 35 is a transverse cross-section view of the tunnel formingapparatus as shown in FIG. 31

FIG. 36 is a side perspective view of the tunnel forming apparatus asshown in FIG. 31 with the sheath inflated and a vascular graft fullyreceived within the sheath.

FIG. 37 is a transverse cross-section view of the tunnel formingapparatus as shown in FIG. 33.

DESCRIPTION

Certain terminology is used herein for convenience only and is not to betaken as a limiting. For example, words such as “upper,” “lower,”“left,” “right,” “horizontal,” “vertical,” “upward,” “downward,” “top”and “bottom” merely describe the configurations shown in the FIGs.Indeed, the components may be oriented in any direction and theterminology, therefore, should be understood as encompassing suchvariations unless specified otherwise. The words “interior” and“exterior” refer to directions toward and away from, respectively, thegeometric center of the core and designated parts thereof. Theterminology includes the words specifically mentioned above, derivativesthereof and words of similar import.

Referring now to the drawings, wherein like reference numerals designatecorresponding or similar elements throughout the several views, anembodiment of an apparatus for use in forming a subcutaneous anatomicaltunnel for implantation of a vascular graft in a patient is shown inFIGS. 1-3. The tunnel forming apparatus, also referred to herein as atunneling device, comprises a tunneling instrument 100 including aproximal handle 102 and a distal tip assembly 50.

An arteriovenous graft suitable for use in this application is describedin commonly owned U.S. Pat. No. 9,585,998, the contents of which arehereby incorporated by reference in their entirety. It is understoodthat the tunnel forming apparatus is also capable of use with othervascular grafts as well as a natural tissue graft or fistula.

An embodiment of the tip assembly 50 is shown in FIGS. 4 and 5. The tipassembly 50 comprises a tip 51 and a swivel connector 58. The tip 51 andthe swivel connector 58 may be constructed of stainless steel, but oneof ordinary skill in the art will recognize that other materials may besuitable to connect an arteriovenous graft to the tunneling device. Onesuch example of an alternative material is a plastic, such as a hardplastic.

Referring to FIGS. 6 and 7, the tip 51 includes a bullet shaped distalend 52 and a longitudinally extending proximal end coupler 54. Theswivel connector 58 comprises a bell-shaped ferrule 59 defining acentral axial channel 63 for rotatably receiving the coupler 54 (FIGS. 8and 9). The proximal end of the coupler 54 defines an internallythreaded axial opening so that the ferrule 59 may be secured to thecoupler 54 by a screw 61 for an axially rotatable swivel connection.

The proximal end of the ferrule 59 is externally threaded 65 forsecuring the tip assembly 50, and associated vascular graft, to theinternally threaded distal end of the tunneling instrument 100. Whenassembled, the swivel connector 58 is rotatable about its longitudinalaxis on the coupler 54 allowing the tip assembly 50 to be threaded intothe tunneling instrument 100 without rotating a connected graft or agraft covered by a sheath. Other conventional methods of fastening theswivel connector 58 to the tunneling instrument 100 include snap-on orclip-on techniques that allow the ferrule 59 to snap or clip into atunneling instrument. These and other fastening techniques arecontemplated to be within the scope of the invention.

A fastening clip may be used to couple a vascular graft 10, or the graftand a sheath 20, to the tip assembly 50 such that the sheath is attachedto and encloses at least the proximal end and a portion of the length ofthe vascular graft. In one embodiment shown in FIG. 10 and generallydesignated at 70, the fastening clip comprises a hollow cylindrical cap70. A distal end of the cap 70 includes a plurality of fingers 72extending radially inwardly into the passage 71 defined by the cap. Thecap 70 is configured to receive and enclose a portion of the proximalend of the arteriovenous graft. Referring to FIGS. 11 and 12, the tip 51includes a smaller diameter portion spaced from the distal bullet-shapedend 52 and forming a peripheral annular groove 56. The annular groove 56is configured to receive the proximal end of the graft, and sheath ifpresent, enclosed by the cap 70. In use, the graft and sheath may becoupled to the tip 51 by passing the graft and sheath through the cap70. The graft and sheath are then secured to the tip 51 by slipping thecap 70 with the graft and sheath over the distal end 52 of the tip 51and axially along the tip 51 until the fingers 72 seat in the groove 56.In this configuration, the proximal end of the graft and sheath areenclosed within the cap 70 and securely within the groove 56 for fixedlypositioning the graft and sheath therein.

Another embodiment of a fastening element for securing an arteriovenousgraft, or the vascular graft and a sheath, to the tip assembly 50 isshown in FIGS. 13-16 and generally designated at 80. In this embodiment,the fastening element comprises a lock ring 80 mounted around a proximalend of the graft, or graft and sheath, for securing the graft in thegroove 56 and preventing axial movement of the graft relative to the tipassembly 50. More particularly, the lock ring 80 may be coupled to thetip 51 by crimping about a pivot pin 81 such that teeth 82 on opposedsurfaces of the free ends of the lock ring 80 engage for enclosing thegraft and sheath within the groove 56 and fixedly positioning the graft,or graft and sheath therein (FIGS. 17 and 18). This arrangement providesfor coupling of a tunneling instrument 100 to an arteriovenous graft 10by a compressive force on the graft for subcutaneously deploying thegraft 10 in a patient. The arteriovenous graft 10 may be surrounded by asheath 20 for drawing both into the subcutaneous tissue cavity in thepatient. The sheath 20 is secured to the tip assembly 50 and surroundsat least a substantial portion of the arteriovenous graft as shown inFIGS. 21 and 22.

FIG. 19 shows yet another embodiment of a fastening element for securingan arteriovenous graft, or the graft and a sheath, to a tunnelinginstrument 100 and is generally designated at 120. In this embodiment,the tip assembly 50 is removed and the fastening element is secureddirectly to the distal end of the tunneling instrument 100. Thefastening element comprises a coupler 120 including a socket 122 and aclip 124 to be connected between a distal end of the tunneling deviceand a proximal end of the graft. The socket 122 includes a hollowcylindrical sleeve 126, a washer 128 and a threaded proximal plug 130for threadably securing the sleeve 126 to an internally threaded end ofthe tunneling device 100. The plug 130 is connected to the proximal endof the sleeve 126 via an opening 127 in the sleeve with a screw 131 andwasher 128 there between. This arrangement allows the plug 130 to rotaterelative to the sleeve 126. The sleeve 126 has opposed partiallycircumferential slots 132 spaced intermediately along the length of thesleeve 126. The proximal end of the clip 124 includes a pair of axialflexible arms 134. Each of the arms 134 has a radially outwardlyextending shoulder 136. The remainder of the clip 124 distally of thearms 134 is generally circular in cross-section.

In use, the plug 130 and connected sleeve of the socket 122 is threadedonto the distal end of the tunneling instrument 100. The proximal end ofthe graft is pushed over the distal portion of the clip 124 for securingthe graft to the clip. The clip 124 and graft are then pushed into thedistal open end of the sleeve 126. This causes the arms 134 to compressinwardly together until the shoulders 136 reach the slots 132 at whichpoint the arms 134 spring outwardly as the shoulders 136 enter the slots132. This fastens the socket 122 and clip 124 together along with theconnected tunneling device and graft. The user can now pull the graftinto the subcutaneous tunnel previously formed by the tunnelinginstrument 100.

Referring now to FIG. 20, another embodiment of a fastening element forsecuring an arteriovenous graft, or the graft and a sheath, directly toa tunneling instrument 100 is shown and generally designated at 90. Thefastening element comprises a frustoconical cup 90 has an axial openingthrough a small diameter externally threaded proximal end 92 configuredfor receiving the graft (Step A). The proximal end of the graft passesthrough the end 92 of the cup 90 (Step B) and is then folded back overthe threads (Step C). The proximal end 92 of the cup 90 is threaded intothe distal end of the tunneling instrument 100 (Step D), such that thelarge diameter open end of the cup 90 is facing distally away from thetunneling device 100 (Step E).

In use, after the distal end of the tunneling instrument 100 emergesfrom the second distal incision, the proximal end of the vascular graftis pulled through the cup 90 and everted back over the periphery of thethreaded end 92 of the cup 90 (Steps B and C). The cup 90 and graft arethen threadably connected with the distal end of the tunneling device100 for securing the end of the graft (Steps D and E). Once connected,the cup 90 is be pulled by the tunneling device 100 along with the graftthrough the anatomical subcutaneous path created by the tunnelingdevice. The cup 90 assists in the passage of the graft into the body bycausing the outward deflection of surrounding tissue upon contacting thefrustoconical cup 90. After the graft is pulled through the tissuetunnel, the cup is removed prior to anastomosis of the graft. It isunderstood that other means for connecting the end of the cone 90 to thetunneling device 92 which do not require threads are suitable.

Referring to FIGS. 23A-23C, a system is shown for implanting anarteriovenous graft (AVG) 10 further comprising a tubular sheath 20positioned over and enclosing at least a substantial portion of theouter surface of the graft during the implantation procedure. Followingimplantation of the arteriovenous graft 10, the sheath 20 is configuredto roll along the graft 10 upon application of a pulling force along thelongitudinal axis of the sheath 10 to extract the sheath.

The sheath 20 comprises a tubular structure that is dimensioned indiameter and length to cover at least a substantial portion of the outersurface of the AVG 10. The sheath 20 can be constructed from any smooth,flexible and compressive biocompatible material. Suitable material canbe porous, non-porous, permeable, or impermeable. Examples of suchmaterials include, but are not limited to, silk, silicone,fluoropolymers such as expanded polytetrafluoroethylene (ePTFE), highdensity polyethylene (HDPE), and other polymers such as polyesters andpolyimides. Various desired configurations may be achieved by varyingfilm materials and characteristics, such as thickness and width. Thesheath 20 may be extruded, for example, directly over a lead body or asa pre-manufactured item subsequently attached to a lead. The sheath 20allows for easier insertion of the graft 10 through the tunneled tissuepath due to the unrestricted and flexible nature of the compressibleouter surface of the sheath. The sheath 20 may be constructed of amaterial that does not excessively flex, so that the sheath 20 absorbsthe tensile force imparted during tunneling as opposed to the graft 10.This will help to prevent damage to the graft 10, which may reduce graftstretching and subsequent graft weeping and seroma formation, and damagethat may allow the graft to kink.

In the embodiment of the implantation system shown in FIGS. 23A-23C, thesheath 20 is doubled over on itself such that the amount of materialused to make the sheath will be at least double the length desired tocover the AVG. The sheath 20 in this embodiment has a “double walled”construction. An inner portion 22 of the sheath 20 extends from aposition proximal of the AVG 10 radially over and axially along the AVGto a position distal of the AVG where the inner portion 22 is foldedback to provide an outer portion 24. The outer portion 24 extendsradially over the inner portion 22 and to a position proximal of the AVG10. When the sheath 20 is extracted by a rolling action, the sheath 20will slide over itself thus reducing the force necessary to extract thesheath. It is understood, however, that an embodiment of the sheath 20may have a sufficiently low coefficient of friction that the sheath canbe removed from the tunnel by pulling the sheath from the tunnel and nota rolling motion.

As shown in FIGS. 23A-23C, the sheath 20 has perforations 30 disposedalong the longitudinal axis of the sheath. The perforations 30 aregenerally oriented linearly in diametrically opposed positions along thelength of the sheath 20. The perforations 30 allow the sheath to tear atthe perforations upon rolling as the sheath 20 is extracted. In anotherembodiment, the sheath 20 may comprise weakened areas of material thatwill tear as the sheath is extracted. During retraction, the sheath 20is drawn axially proximally relative to the AVG 10 to retract the sheathfrom over the AVG. The pulling force retracts the sheath 20 from thedistal end and progressively proximally with the outer sheath 24 movingover the inner sheath 22 in a rolling manner.

Referring to the embodiment shown in FIGS. 24A and 24B, the sheath 20 isdrawn axially proximally relative to the AVG 10 to retract the sheathfrom over the arteriovenous graft by the pulling force provided by amoveable tether 40. The tether 40 extends axially from adjacent aproximal end of the arteriovenous graft to an opposite distal end of thegraft where the tether 40 joins the outer portion 24 of the sheath 20 ator beyond the distal end of the graft 10. The tether 40 extendssufficiently proximally externally to the first incision so that it canbe pulled upon for retracting the sheath 20. The tether 40 is pulledupon to retract the sheath 20 from the distal end and progressivelyproximally with the outer sheath 24 moving over the inner sheath 22 in arolling manner. The tether 40 may be a plastic thread or a metal wire.

Referring to the embodiment shown in FIGS. 25A-25C, the sheath 20 is asingle layer having perforations 30 disposed along the longitudinal axisof the sheath. The perforations 30 are generally oriented linearly inclose parallel relation along the length of the sheath 20. Theperforations 30 allow the sheath to tear at the perforations uponrolling as the sheath 20 is extracted. The tether 40 extends axiallyfrom adjacent a proximal end of the arteriovenous graft to an oppositedistal end of the graft where the tether 40 joins the sheath 20 betweenthe perforations 30 at or beyond the distal end of the graft 10. Thetether 40 extends sufficiently proximally externally to the firstincision so that it can be pulled upon for retracting the sheath 20. Thetether 40 is pulled upon to retract the strip of the sheath 20 betweenthe perforations 30.

When the arteriovenous is subcutaneously located as desired, the tether40 or the sheath 20 itself is pulled. FIGS. 23B, 24B and 25B show thepulling force as depicted by arrows. The pulling force moves the sheath20 proximally which, in one embodiment, causes the outer sheath 24 toslide over the inner sheath 22. As the sheath 20 rolls proximally, thesheath is torn at the perforations 30. As the pulling force continues,the sheath 20 will continue to move proximally until the sheath 20 isextracted from the first incision and the arteriovenous graft 10 isuncovered.

The sheath 20 may be coated on the outside surface with a lubricioussubstance to provide a low coefficient of friction, aiding movement ofthe sheath 20 and graft 10 through tissue when pulled by a tunnelinginstrument. This will minimize tissue drag and tissue trauma duringinsertion of the arteriovenous graft 10 or removal of the sheath 20after implantation. The lubricant will also allow the sheath 20 to slidesmoothly across itself. Solid lubricants (i.e. graphite, waxes,silicone), fluid lubricants (i.e. hydrocarbon oils, silicone oils), gels(i.e. hydrogel) or any other biocompatible material known in the art maybe used. In one embodiment, the sheath 20 can be coated or wettedimmediately before implantation by the user. In another embodiment, theinvention comprises a kit comprising a sheath and a wetting agent forwetting the sheath 20. In another embodiment, the invention comprises akit comprising a sheath 20, an arteriovenous graft 10 and a wettingagent for wetting the sheath.

The sheath 20 may be attached to at least the distal end of thearteriovenous graft by mechanical, rail or interference fit, mechanicalstructures, heat bonding or by a biocompatible adhesive or othersecuring means. Example adhesives are thermoplastic fluoropolymers, suchas fluorinated ethylene propylene (FEP). The sheath may also be attachedto the arteriovenous graft following its manufacture as a separatecomponent.

The system and method for implanting the arteriovenous graft, includinga sheath enclosing the graft during implantation, have many advantages,including atraumatic implantation of an arteriovenous graft andsubsequent extraction of the associated sheath. The sheath provides aflexible, compressible outer surface for the graft that may allow foreasier insertion of the graft into the tissue cavity with less trauma,less friction, and less drag during placement. Thus, the system andmethod described herein reduce damaging forces to surrounding tissuesassociated with the implant procedure and minimize the resultant traumato this tissue and its healing response. Due to the smoothness andcollapsible low profile of the sheath, the tunneling procedure may befaster and easier to use, in addition to being less traumatic to tissue.

FIG. 26 shows an embodiment of a tunneling instrument generallydesignated at 150. The shaft 152 defines an axial opening extendingthrough its entire length. The distal end of the shaft 152 has aplurality of holes 156 in fluid communication with the axial openingthrough the shaft 152. This configuration allows infusion or aspirationof a fluid from a fluid source delivered through the shaft 152 to thetip 154. During advancement of the tunneling instrument 150 through thesubcutaneous tissue, fluid can be infused from the fluid source andthrough the distal shaft holes 156. The infused fluid exits the shaftholes 156 adjacent to the distal end 153 of the tip 154 for lubricatingthe tissue passage. Examples of fluid for use in this applicationinclude, but are not limited, to phosphate-buffered saline, saline andbuffered saline as well as gas.

Referring to FIG. 27, another embodiment of a tunneling instrument fordelivering fluid is shown and generally designated at 160. In thisembodiment, the tip 162 or nose section has a plurality of openings 164.When the tip 162 is fastened to the distal end of the shaft 152, theaxial opening through the shaft is in fluid communication with the holes164 in the tip 162. In use, the tunneling apparatus 160 deliverspressurized fluid, such as air, from a fluid source through the shaft152 and through the holes 164 in the tip 162 during advancement of thetunneling apparatus 160 through subcutaneous tissue. The pressurizedfluid exits the tip 162 in the direction of advancement of the tunnelingapparatus 160 for aid in dissecting tissue during the tunnelingprocedure.

Yet another embodiment of a tunneling apparatus is shown in FIG. 28 andgenerally designated at 170. The tunneling apparatus 170 comprises arigid shaft 172 with a magnetic tip 174, or nose section, at a distalend 173 of the shaft. As with other tips described herein, the magnetictip 174 has an elliptical or circular shape that facilitates the bluntdissection inherent in the tunneling procedure. As shown in FIG. 28, amagnetic wand 176 is provided for engaging the tip 174 across the skin158 boundary. During the tunneling procedure, the tip 174 is advancedthrough the subcutaneous tissue by moving the wand 176 along the surfaceof the skin 178.

An embodiment of a self-guiding tunneling apparatus is shown in FIG. 29.In this embodiment, markers 92 placed on the skin 94 of a patientindicate a predetermined path for the anatomical tunnel for placement ofa vascular graft 10. The markers 92 identify proper placement of atunneling device (not shown) beginning from an incision 96 into thebody. The user follows the markers 92 in navigating the tunneling devicethrough the body, thereby increasing the accuracy of the procedure byfollowing well-established practices of guide wire navigation.

An embodiment of a locking mechanism for use with a looped vasculargraft is shown in FIGS. 30 and 31 and generally designated at 800. Thelocking mechanism 800 is for use with a pair of arcuate tunneling rods802 schematically shown in FIG. 30. The rods 802 are arranged to be slidalong curved paths that mirror one another. The length of the rods 802depends on the procedure, and particularly on the length of the vasculargraft to be inserted. The distal end of each rod 802 is inserted intothe exposed tissue at an incision 804. The rods 802 are advanced to apoint spaced from the incision 804 with the proximal ends 803 of therods 802 remaining outside of the body. The distal ends 805 of the rods802 each carry a portion of the locking mechanism 800. In assembling thepair of rods 802, the locking mechanism 800 components are joinedsubcutaneously where the distal ends 805 of the rods 802 come together.

A further embodiment of a tunneling apparatus is shown in FIG. 32 andgenerally designated at 180. The tunneling apparatus 180 comprises arigid shaft 182 with a tip 184, or nose section, at a distal end 183 ofthe shaft. In this embodiment, the shaft 182 is fabricated in a helicalshape. Thus, the anatomical tunnel formed through the tissue follows ahelical path. The vascular graft is then placed within the tissue tunnelin the form of a helical spring.

Yet another embodiment of a tunneling apparatus is shown in FIGS. 33-37and generally designated at 400. The tunneling apparatus 400 comprises aguide wire 402 and an elongated tubular sheath or conduit 404. The guidewire 402 is substantially rigid for use as a tunneling instrument increating a subcutaneous tissue path in the patient. The diameter of theguide wire 402 is smaller in comparison to a conventional tunnelinginstrument to reduce the trauma to the surrounding tissue as theguidewire is pushed through the tissue. The sheath 404 is mounted overthe guide wire 402 and encloses the guide wire during a tunnelingprocedure into the tissue of a patient.

The sheath 404 is formed from a double layer of thin flexible,compressible material closed at both ends and is radially expandable.Accordingly, the sheath 404 has a contracted deployment state, in whichthe sheath is compressed against the guide wire 402 for use as aninsertion tool assembly, and a radially expanded inflated state, whichthe sheath 404 assumes upon being inflated with a fluid, including aliquid or a gas. The guide wire 402 functions as a means for supportingthe sheath 404 in its contracted state during the tunneling step whenthe tissue is traversed. After the creating the tunnel in tissue, thesheath 404 is inflated, expanding radially outwardly pushing against thetissue walls and providing a clear central hole. In the inflatedcondition, the sheath 404 is configured for providing an opening of adiameter through which a distal end 403 of the guide wire 402 may bewithdrawn for receiving a vascular graft 10 with the application of areasonable level of axial force. The application of radial force asopposed to longitudinal force in forming the area of the subcutaneoustunnel minimizes trauma to the surrounding tissue and therefore reducesthe rate of swelling, pain, and bleeding post-procedure. Thisfacilitates immediate or early cannulation of an implanted vasculargraft. Additionally, minimizing the force on the graft 10 duringimplantation will help to prevent damage to the graft, which may reducegraft stretching and subsequent graft weeping and seroma formation, andhelp prevent graft kinking.

The sheath 404 may be fabricated from polyethylene, polyvinyl chloride,or other suitable materials well known to those skilled in the art.These materials may further include, but are not limited to, Mylarribbon, Teflon ribbon, and polypropylene. The smooth outer surface ofthe material of the sheath 404 may allow the tunneling device 400 tohave a low coefficient of friction. The result is easier insertion ofthe guide wire 402 through the tissue with less trauma, less friction,less blunt dissection and less drag during placement. Due to thesmoothness and collapsible low profile of the sheath 404, the sheathdoes not substantially increase the outside diameter of the tunnelingapparatus 400 for deployment. The tunneling apparatus 400 may thus befaster and easier to use, in addition to being less traumatic to tissue.The sheath 404 may also be coated with a lubricous material to furtherdecrease its coefficient of friction and facilitate insertion of thetunneling device 400. The coating aids movement of the sheath 404 andguide wire 402 through the tissue while minimizing tissue drag andtrauma during insertion or during sheath 404 removal after implantation.It is understood that a wide variety of coatings are available,including therapeutic agents for delivery of therapeutic materials.

In use, two spaced incisions are first made through the patient's skininto underlying tissue. The distal end 403 of the guide wire 402 withthe sheath in the deployment state is inserted into a first incision andthen forced horizontally through the subcutaneous tissue along a pathuntil the distal end 403 exits the second incision. The distal end 403of the guide wire 402 is then attached to a proximal end of the vasculargraft 10 by the surgeon, such as, for example, using simple mechanicalmeans, a compression fit collar, staples or sutures or other fasteningtechniques acceptable for implantation within the tissue of the body.After attachment of the graft 10 to the guide wire 402, the sheath 404is inflated with fluid forcing the sheath against the dissected tissuedefining the tunnel. The expansion of the sheath 404 forms an internalpassage through the sheath that is sufficiently large to allow thesubsequent withdrawal of the guide wire 402. The guide wire 402 isretracted proximally, which simultaneously draws the attached graft 10into and through the lumen of the inflated hollow sheath 20 until theproximal end of the graft 10 exits the first incision. The inflatedsheath 204 allows the surgeon to easily pull the vascular graft 10through the internal lumen defined by the sheath 204, which issubstantially oversized in comparison to the outside diameter of thevascular graft 10. Once the graft 10 has been drawn to the site of thefirst incision, the proximal end of the graft 10 is disconnected fromthe distal end 203 of the guide wire 202.

Next, the sheath 204 is deflated and extracted from the subcutaneoustissue path without extracting the graft 10. Specifically, the surgeonholds the graft 10 in place by grasping a distal end of the graftextending from the second incision and pulls the sheath 204 through thefirst incision. The graft 10 remains within the anatomic subcutaneoustunnel. With the sheath 204 removed, the tissue collapses against theouter surface of the graft 10. The surgeon now forms anastomoses at eachend of the graft 10 by suturing the ends of the graft to a blood vesselat the desired locations.

The embodiments of the tunneling apparatus as described herein are shownin use for procedures with a vascular graft suitable for implantation inthe body and used to reestablish or redirect the flow of blood beyondthe blockage area. It is understood that the several tunneling apparatusdescribed and shown herein may be used in other surgical implantationprocedures requiring placement of the vascular graft within thesubcutaneous tissue. One of ordinary skill in the art will recognizethat the embodiments of the tunneling apparatus as described are notdirected to a specific vascular graft design, but are genericallyapplicable to many different types of vascular grafts, which may be asynthetic graft constructed from different materials or a natural tissuegraft.

The tunneling apparatus and methods as described have many advantages,including a reduction of friction and resistance, and related tissuedamage, during the passage of the tunneling device when forming a ananatomical tunnel. The tunneling apparatus and methods may help toreduce swelling and damage to the surrounding tissue, which wouldfacilitate immediate or early cannulation of a subsequently implantedvascular graft.

We claim:
 1. An apparatus for subcutaneous implantation in a patientusing a tunneling instrument including a shaft having a proximal end anda distal end, the implantation apparatus comprising: a vasculararteriovenous graft having a proximal end and a distal end and a lengthbetween the proximal end and the distal end; a connector adapted tocouple the distal end of the tunneling instrument and the proximal endof the graft, the connector comprising a tip, a first end of the tipconfigured to be received within the proximal end of the graft, a clipfor securing the graft to the tip, and a coupler for a rotatableconnection of the tip to the tunneling instrument such that the tip isrotatable about its longitudinal axis relative to the coupler tofacilitate attachment of the graft to the tunneling instrument.
 2. Theimplantation apparatus as recited in claim 1, wherein the couplercomprises a screw thread formed on an external surface for connection ofthe coupler to the tunneling instrument.
 3. The implantation apparatusas recited in claim 1, wherein the coupler comprises a ferrule definingan axial passage for rotatably receiving a proximal end of the tip. 4.The implantation apparatus as recited in claim 1, further comprising aremovable sheath covering the graft.
 5. The implantation apparatus asrecited in claim 4, wherein the sheath is configured to substantiallycover the length of the graft.
 6. The implantation apparatus as recitedin claim 1, wherein the tip comprises a body including an intermediateportion having a reduced diameter forming a circumferential groovearound a periphery, and wherein the clip is positioned in the groove, aportion of the graft being positioned between the clip and the tipwithin the groove, the clip being crimped about the tip to fix the graftto the tip.
 7. The implantation apparatus as recited in claim 6, whereinthe clip is sized and shaped to provide a snap-fit connection within thegroove.
 8. The implantation apparatus as recited in claim 1, wherein thetip is adapted to be removably attached to the distal end of thetunneling instrument, and wherein the connector is configured forconnecting the graft to the tunneling instrument upon removal of thetip.
 9. The implantation apparatus as recited in claim 8, wherein thecoupler comprises a frustoconical cone having an axial opening forreceiving the graft, a length of the cone including a screw threadformed on an external surface for connection of the cone to thetunneling instrument, wherein a portion of the graft is positionedbetween the threads of the cone and the tunneling instrument to fix thegraft to the tip.
 10. The implantation apparatus as recited in claim 8,wherein the coupler comprises a hollow sleeve for rotatable connectionto the tunneling instrument, and a plug received within the proximal endof the graft, the sleeve configured for receiving the plug such that aportion of the graft is positioned between the plug and the sleeve tofix the graft in the sleeve.
 11. The implantation apparatus as recitedin claim 1, wherein the longitudinal coupler is adapted to be attachedto a synthetic vascular graft.
 12. The implantation apparatus as recitedin claim 1, wherein the longitudinal coupler is adapted to be attachedto a natural tissue vascular graft.
 13. The implantation apparatus asrecited in claim 1, wherein the longitudinal coupler is adapted to beattached to an arteriovenous graft.
 14. An implantable device forsubcutaneous delivery in a patient using a tunneling instrumentincluding a shaft having a proximal end and a distal end, theimplantable device comprising: a vascular graft having a length, adistal end, a proximal end, an outer surface and a longitudinal axis;and a sheath having a length and being positioned over a substantialportion of the outer surface of the vascular graft, the sheath havinglongitudinally spaced perforations along the length of the sheath forpermitting tearing of the sheath, wherein the sheath is configured toevert upon application of a longitudinal force to the sheath followingimplantation of the vascular graft to cause the sheath to move in aproximal direction during removal of the sheath from the implantedgraft, and wherein upon eversion and exceeding a tearing strength thesheath tears progressively along the perforations that are generallyoriented in a linear arrangement along the length of the sheath.
 15. Theimplantable device as recited in claim 14, wherein two rows ofperforations are generally oriented circumferentially opposite to oneanother.
 16. The implantable device as recited in claim 14, wherein tworows of perforations are generally oriented adjacent and parallel to oneanother.
 17. The implantable device as recited in claim 14, furthercomprising tether connected to the sheath for applying a pulling forcein a proximal direction.
 18. The implantable device as recited in claim17, wherein the one end of the tether is attached to the sheath at aposition adjacent to the distal end of the sheath.
 19. An implantabledevice for subcutaneous delivery in a patient using a tunnelinginstrument including a shaft having a proximal end and a distal end, theimplantable device comprising: a vascular graft having a length, adistal end, a proximal end, an outer surface and a longitudinal axis;and a sheath having a length and being positioned over a substantialportion of the outer surface of the vascular graft, the sheath havinglongitudinally spaced perforations along the length of the sheath forpermitting tearing of the sheath, wherein the sheath is folded back onitself to provide a double wall including an inner portion and an outerportion, and wherein the sheath is configured to slide over itself uponapplication of a longitudinal force to the sheath following implantationof the vascular graft to cause the sheath to tear along the perforationsand move in a proximal direction during removal of the sheath from theimplanted graft thus reducing the force necessary to extract the sheath.20. A tunneling device for use in subcutaneous placement of a vasculargraft in a patient, the tunneling device comprising: a guide wire; ahollow inflatable conduit coaxially surrounding the guide wire over asubstantial portion of its length, the conduit in a deliveryconfiguration collapsing against the wire due to confining pressure wheninserted subcutaneously into a body, wherein inflation of the conduitradially expands the conduit to a deployed configuration and spaces theconduit from the wire over substantially the full length of the wire andpreventing collapse of the subcutaneous tissue inwardly against thewire, and wherein the graft may be introduced into the conduit while theconduit is inflated.